Agree with Goodbeer. Downtown San Jose (many options available with most major chains represented), unless you are here for more than one day then consider staying in SF especially since you will have a group and a bus. Are you flying into SJC or SFO?
There is only one luxury hotel at Santana Row. I would not stay there for your needs.
You can ask the SJ forum but the regular posters usually see these thread as well. November will probably chime in. Downtown SJ is still the general recommended. There is no nightlife around the stadium.
Yes, downtown SJ would be my choice too. Plenty of hotel options. Lots of restaurants and bars. Easy transport to the stadium via light rail.
It will be 4 days and a group between 60 and 80 people
Stay in SF and book a party bus each way for the game.
Yes agree with Claire to stay in SF and charter bus to and from the game. You don't want to spend that much time in the South Bay.